Light is made up of waves. Some waves have different sizes. The distance between the top of one wave and the top of the next wave is called the "wavelength". Different colors of light have different wavelengths. Red light has long waves. Purple light has short waves. Green light is in between. The wavelength of green light is around 550 nanometers (nm). This is the same as 5,500 Ångströms (Å). Light with short waves has more energy than light with long waves. Purple light has more energy than red light. Original Windows to the Universe artwork by Randy Russell.